A TiN coating layer having a low friction coefficient, a high hardness and a good corrosion resistance is widely applied as a decorative coating layer, a wear-resistant coating layer or a corrosion-resistant coating layer. Currently, TiN coating layers have been prepared by many researchers through technologies such as reaction thermal spraying, chemical vapor deposition (CVD), physical vapor deposition (PVD), an arc plating and the like, and the deposition process, microstructure and properties of the coating layers are studied. The TiN coating layers prepared by CVD, PVD or the like are relatively thin, and thus the mechanical property of the coating layers are reduced; and although thicker TiN coating layers may be prepared by a thermal spraying reaction technology, more pores exist in the coating layers and the coating layers have large brittleness, rendering quality of the coating layers not easy to be controlled. By directly spraying TiN powder with a plasma spraying technique, a relatively thick coating layer can be prepared within a short time; meanwhile, oxidation of TiN occurs during the spraying process to form an oxide phase of Ti, which can improve the toughness of the coating layer.
The plasma spraying technique is widely used for preparing metals, ceramics and composite coating layers to resist abrasion, corrosion and high temperature. During the spraying process, microscopic defects such as oxides and pores tend to be generated because melted particles chemically react with the surrounding medium during the melting and flight process as well as the process of contacting with a matrix surface, resulting in the spraying material to be oxidized; and also because pores are generated inevitably among the molten particles due to successional stacking of the particles as well as rebounding and dissipation of a part of the particles. Microscopic defects such as oxide content and porosity in the coating layers are important standards for evaluating quality of the coating layers. Influence of the porosity and control of the oxide during the plasma spraying process on the properties of the coating layers is studied by scholars, and the microstructure and properties of the coating layers can be improved significantly by controlling appropriate process parameters. Since TiN tends to be decomposed and oxidized under a high temperature and has a large activity, it reacts with other mediums during the plasma spraying process to form an oxide of Ti. The oxide content in the TiN coating layer has a direct influence on the properties of the coating layer since the oxide phases of Ti have a lower hardness and strength than the TiN phase. Fracture toughness is an ability of a material to resist fracture failure. The fracture toughness of the coating layer is measured by an indentation method, which has been widely applied. The hardness and fracture toughness of the coating layer are main indicators for the coating layer to resist crack propagation and fracture, which have a direct impact on the service performance and life of the coating layer.
Currently, the TiN coating layers are prepared by technologies such as the reaction thermal spraying, the chemical vapor deposition (CVD), the physical vapor deposition (PVD), the arc plating and the like, and the deposition process, microstructure and properties of the coating layers have been studied by many researchers. The TiN coating layers prepared by CVD, PVD, etc. are relatively thin, thus the mechanical property of the coating layers is reduced; and although relatively thick TiN coating layers may be prepared by a thermal spraying reaction technology, more pores exist in the coating layers and the coating layers have large brittleness, rendering quality of the coating layers not easy to be controlled. However, by directly spraying TiN powder with plasma, not only the thickness of the coating layer can be ensured, but also the toughness of the coating layer can be improved due to the oxide phase of Ti in the TiN coating layer, thus the coating layer having excellent hardness and toughness can be obtained.